class_docstr: Lightweight immutable Dataframe similar to Pandas Dataframe.
code: def n_columns(self) -> int:
      return len(self._columns) if self._columns else len(self._rows[0])
  
imports: import itertools
  import json
  from typing import Any, Callable, Optional, Sequence, Tuple, Union
  from collections import namedtuple
  import numpy
  from tensorflow.python.compiler.tensorrt.model_tests import model_handler
  import tensorflow.python.compiler.tensorrt.trt_convert
  from tensorflow.python.platform import tf_logging
label_desc: Use image node_id 3 for calling the DataFrame obj's underlying member method code with example usage: obj.n_columns() and returns: unknown